My prior invention, disclosed in the above-identified patent application, is a continuously-variable transmission with variable inertia flywheels for energy storage. A main pair of the variable inertia flywheels was provided for primary energy storage and used radially displaceable solid masses for varying moment of inertia. A secondary pair of control flywheels was provided for controlling changes in the moments of inertia of a primary pair of flywheels. The secondary control flywheels also provided some supplemental energy storage. Liquid could be added to and removed from the secondary control flywheels to vary their moments of inertia for control purposes. The primary flywheels were selectively coupled through gearing to an input shaft and/or an output shaft to provide energy storage with the continuously-variable transmission.
The mechanically positionable solid masses of the primary flywheels and the associated gearing of the transmission of my prior invention provided high operating efficiency. However, the major drawback of that device was its complexity and the possibility of damage to moving components, primarily the radially displaceable solid members used to vary moment of inertia of the primary flywheels.
The present invention is directed to energy storage systems, and particularly to continuously-variable transmissions incorporating such systems, where moment of inertia variations of the flywheels are accomplished hydraulically.
Energy storage systems utilizing liquid for moment of inertia variation and continuously-variable transmissions incorporating such systems can have certain possible advantages and disadvantages when compared with my prior invention using solid weight members.
A first possible advantage is that movement of liquid in such flywheels is much more easily controlled. Additional flywheels, such as the secondary control flywheels in my prior invention, or alternative devices, such as mechanically geared or continuously-variable transmissions, are not required for control of the primary flywheels.
A second possible advantage is that when such flywheels are used in an energy storage transmission, the transmission can be not only continuously-variable, but infinitely variable in the lowest speed range, permitting drive in either the forward or reverse direction without shifting. This would be a useful feature in vehicles such as tractors, bulldozers, backhoes, locomotives, etc. Inertia variations in such flywheels are not fixed and symmetry does not have to be maintained as was the case with the solid mass flywheels of my prior invention. Energy can then be extracted or stored when the output torque is split equally between the forward-driving and reverse-driving flywheels. However, the portion of the stored energy that can be used with this gearing is rather small.
A third possible advantage is that the simpler of my liquid filled flywheels designs should permit a high ratio of maximum to minimum moments of inertia and a substantial range of speed, despite the second possible disadvantage listed below.
A fourth possible advantage is that the liquid used as a movable mass is not subject to damage, unlike flexible strip used in my prior invention.
A fifth possible advantage is that flywheel housing stresses do not increase as rapidly with speed as they do with solid masses because the quantity of liquid and its contribution to these stresses are both generally reduced as speed increases.
A sixth possible advantage in some liquid mass flywheel designs is that space can be saved by locating many of the gears and clutches in the centers of such flywheels.
A seventh possible advantage is that output energy can be extracted directly from both flywheels with some designs, although efficiency is liable to be reduced.
An eighth possible advantage is that the speed of one or both flywheels can be limited by continuing to admit liquid after the flywheel is filled. This permits extension of the lowest speed range. Energy can be extracted from the overflow by directing it into a turbine or equivalent device.
A ninth possible advantage is that braking energy can be absorbed in any speed range, even after the energy storage capacity is reached, by allowing the excess liquid to overflow.
Energy storage system employing liquid filled variable inertia flywheels may suffer from certain disadvantages.
A first disadvantage is that hydraulic devices are required to extract energy from the flywheels and these are generally less efficient that mechanical devices.
A second possible disadvantage is that the speed range and/or the energy available for output are reduced when simple devices are used to extract energy. This is because no energy is exchanged between flywheels through the control systems. All of the energy required to move a flywheel mass inward is supplied from the same flywheel, reducing the amount of energy available from that flywheel for output. The only purpose then served by a second flywheel is that it permits starting from a stop or braking to a complete stop.
A third possible disadvantage is that some hydraulic designs are also mechanically complicated and they require bearings subjected to heavy loads from centrifugal forces.
A fourth possible disadvantage is that the entire centrifugal load produced by the liquid is carried solely by the flywheel housings whereas the mechanical weights in the prior invention were capable of supporting a major portion of the centrifugal load. Flywheel housing stresses may be a more severe limitation on speed and energy storage than with the prior invention despite the relatively lower density of the liquid compared to the solid weights.
A fifth possible disadvantage is that the lower density of most liquids, compared to the solid flywheel masses of the prior invention, and the speed limitations imposed by the hydraulic flywheels, may result in a bulkier apparatus than systems employing solid movable masses, despite the ability to locate portions of the gearing within the flywheels themselves in the hydraulic systems.